There are innumerable variations of standard metol-hydroquinone formulas and these may he found in the literature issued by film manufacturers.
In general, the ratio of metol to hydroquinone is 1:2 for films and 1:3 or 1:4 for papers. If the photographer wants more contrast, he can get it by increasing the amount of hydroquinone or vice-versa.
The amount of metol should not be increased or decreased without a corresponding change in the amount of carbonate, since metol has an acid reaction and an increased amount of metol may lower the pH of the solution and thus lower the activity of the developer, even though more developing agent is actually present.
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For tray use, dilute with an equal volume of water and develop about 7 minutes at 18.5°C. For tank use, dilute with three parts of water and develop 12 to 16 minutes, depending on the contrast desired.